1. Field of the Invention:
The present invention relates to an automatic transmission for use in an automobile.
2. Prior Art:
The performance of an automatic transmission greatly depends on characteristics of fluid-pressure differential cylinders for shift and select operations of the transmission, which cylinders are operative as actuators for displacing a shift lever.
As shown in Japanese Patent Laid-open Publication Nos. 58-146722 and 60-146953, for example, a solenoid-operated valve used to control a fluid-pressure differential cylinder is controlled periodically by a pulse signal while regulating the duty factor of the pulse signal to eventually control the mechanical output of the cylinder.
The pulse signal used in the disclosed valve control has a pulse repetition frequency (e.g. 40 Hz) equal to an on-off response time of the solenoid-operated valve. Thus, the pulse repetition period is equal to 25 m sec. in which instance the minimum pulse width is 6 m sec. or more and hence the pulse duty factor is regulated such that it varies to increase from a minimum value corresponding to this minimum pulse width. Where the pulse signal has a pulse repetition period of 25 m sec. and a minimum width of 6 m sec., each pulse (i.e., a single cycle of on-off operation of the valve) causes the piston to be displaced about 0.1 mm even though the displacement is related to the volume of the cylinder, the pressure of the working fluid, etc. This means that the output of the cylinder can be regulated stepwise by about 0.1 mm at a minimum and hence the resolution of the cylinder output is about 0.1 mm.
When the fluid-pressure cylinder having such resolution of the order of 0.1 mm is used, shift and select positions are determined with an error of about 0.2 mm, thus causing deterioration of the performance of an automatic transmission in which the cylinder is employed.
Further, two such fluid-pressure differential cylinders are disposed separately for effecting shift and select operations, respectively, of the automatic transmission, and they are connected to the corresponding pipings.
Such separate piping requires an increased number of attachments or fittings and hence the piping work is complicated as a whole.
Moreover, the piston of the cylinder is not provided
e position, positional adjustment of a piston rod and a shift lever must be carried out by the trial-and-error method.
Such trial-and-error positional adjustment is tedious and time-consuming.